The present invention relates to a superfinishing apparatus using an abrasive film and, in particular, to an apparatus for superfinishing small or fine objects that are difficult to grind such as mechanical parts having a complex configuration.
FIG. 7 shows an example of a conventional superfinishing apparatus using an abrasive film 4 in the form of an elongated tape. The film 4, which is successively fed out from a feed spool 21 by wind-up force of a wind-up spool 22, is led to a backup roll 2 by a guide roll 23. Then, the film 4 is pressed at its grinding surface against a workpiece 24 by the backup roll 2 and, through axial vibrations applied to the backup roll 2, the film grinds the surface of the workpiece 24 to achieve superfinishing thereon. After the grinding, the film 4 is wound up around the wind-up spool 22 via a guide roll 25.
The film 4 is introduced necessarily vertically with respect to the axis of the backup roll 2. Therefore, depending on the shape of the workpiece 24, it would, in some cases, be difficult or impossible to grind the workpiece with ordinary superfinishing apparatuses.
For example, in the case of a T-shaped gear 26 shown in FIG. 8(A), which is a part used for differential gears or the like relating to the power transmissions of automobiles, attempting to grind even the root of the shaft in the process of grinding the gear teeth would cause the film feed mechanism 27 to make contact with the shaft. Also, attempting to grind even the root portion of the shaft in the process of grinding the shaft as shown in FIG. 8(B) would likewise cause the film feed mechanism 27 to make contact with the gear teeth, such that there would occur a portion of a distance d from the corner portions that cannot be ground.
Furthermore, in grinding an article having a complex configuration such as a crank 28 shown in FIG. 8(C), since the film feed mechanism 27 makes contact more often with portions other than the grinding surface of the crank 28, it would be difficult to grind small or fine portions of the crank 28.
Interference between the article and the film feed mechanism 27 occurs to one side surface of the film 4. Therefore, if the film 4 can be slid transversely and moved as it is until the time immediately before being introduced to the backup roll 2, then the film feed mechanism 27 can be prevented from making contact with the article on a side opposite to the side toward which the film 4 has been slid.
In order to slide the traveling path of the film 4, there arises a need for a device which can change the traveling direction of the film. One solution is a method of changing the traveling direction of the film 4 by winding the rear surface (the surface that is not used for grinding) of the film 4 around the surface of a cylindrical member 29, as shown in FIG. 9.
In this case, if the inclination (lead angle) of the center axis of the cylindrical member 29 with respect to the original traveling direction of the film 4 is assumed as .crclbar. (rad), and if the film 4 is wound around the surface of the cylindrical member 29 at an angle of 2.pi. (rad), i.e., 180.degree., then the traveling direction of the film 4 is changed by an angle of 2.crclbar. (rad). It is noted that the changing angle 2.crclbar. is not affected by the size of the cylindrical member 29.
If two cylindrical members 29 are provided, the forward and backward traveling directions of the film 4 can be changed with respect to the backup roll.
Further, if the traveling direction of the film 4, which has once been changed, is re-changed to the same direction as the original traveling direction by winding the film 4 around another cylindrical member 29 at the same lead angle .crclbar., then the traveling direction of the film 4 can be translated transversely.
If the traveling direction of the film 4 can be translated transversely as described above, then the film feed mechanism 27 will not interfere with the parts shown in FIG. 8, and thus the grinding work up to end portions is possible.
Furthermore, since the feed direction of the film 4 and the axial direction of the backup roll 2 will not vary, most of the conventional grinding apparatuses and equipment therefor can be utilized.
However, using a plurality of cylindrical members 29 for changing the traveling direction of the film abrasive would cause the mechanism to become more complex, which results in increased costs.
Also, it is possible that the member for changing the traveling direction of the film abrasive may itself interfer with the article to be ground or that a change of the traveling direction hinders the abrasive film from smoothly traveling, contrary to what is expected.